What is the medical management for hypernatremia?

Medical Management of Hypernatremia

The medical management of hypernatremia requires careful correction of water deficit at a rate not exceeding 0.5 mmol/L per hour or 10-12 mmol/L per 24 hours, with treatment tailored to the underlying cause and volume status. 1, 2

Classification and Diagnosis

Hypernatremia is defined as serum sodium concentration >145 mmol/L and can be classified as:

• By severity:

  • Mild: 146-150 mmol/L
  • Moderate: 151-155 mmol/L
  • Severe: >155 mmol/L

• By volume status:

  • Hypovolemic: Water and sodium losses with greater water loss
  • Euvolemic: Pure water loss
  • Hypervolemic: Sodium gain exceeding water gain

Diagnostic Approach

1. Exclude pseudohypernatremia
2. Confirm glucose-corrected sodium concentrations
3. Determine extracellular volume status (hypovolemic, euvolemic, hypervolemic)
4. Measure urine sodium levels and osmolality
5. Assess ongoing water losses
6. Check for other electrolyte disorders

Management Principles

1. Calculate Water Deficit

Water deficit (L) = Total body water × [(Current Na⁺/140) - 1]

• Total body water = 0.5-0.6 × body weight (kg) for adults

2. Determine Correction Rate

• For chronic hypernatremia (>48 hours):

  • Maximum correction rate: 0.5 mmol/L/hour or 10-12 mmol/L/day 2

• For acute hypernatremia (<48 hours):

  • More rapid correction may be safe 1
  • Monitor for cerebral edema

3. Volume-Specific Management

Hypovolemic Hypernatremia

• First step: Restore intravascular volume with isotonic fluids (0.9% NaCl)
• Second step: Correct free water deficit with hypotonic fluids (0.45% NaCl or D5W)
• Common causes: Gastrointestinal losses, burns, excessive sweating, osmotic diuresis

Euvolemic Hypernatremia

• Primary treatment: Replace free water deficit with hypotonic fluids
• Common causes: Diabetes insipidus (central or nephrogenic), inadequate water intake
• For central diabetes insipidus: Consider desmopressin
• For nephrogenic diabetes insipidus: Address underlying cause, consider thiazide diuretics

Hypervolemic Hypernatremia

• Primary treatment: Increase free water and enhance sodium excretion
• Common causes: Iatrogenic sodium administration, primary hyperaldosteronism
• Approach: Loop diuretics plus free water replacement

4. Fluid Selection

• Severe hypernatremia with symptoms: Initial IV hypotonic fluids (D5W or 0.45% NaCl)
• Mild to moderate hypernatremia: Oral or enteral free water if possible
• With volume depletion: Initial isotonic fluids followed by hypotonic fluids

Monitoring and Adjustments

• Check serum sodium every 2-4 hours during initial correction
• Adjust fluid rate based on sodium measurements
• Monitor for signs of cerebral edema during correction
• Assess for improvement in neurological symptoms

Special Considerations

• Diabetes insipidus:

  • Central: Treat with desmopressin
  • Nephrogenic: Address underlying cause (medication review, correct hypokalemia)

• Medication-induced hypernatremia:

  • Review and adjust medications (lithium, amphotericin B, demeclocycline)

• Elderly patients:

  • More susceptible due to impaired thirst mechanism
  • May require lower correction rates due to higher risk of complications

Common Pitfalls

• Correcting sodium too rapidly in chronic hypernatremia, risking cerebral edema
• Failing to account for ongoing losses when calculating replacement needs
• Not addressing the underlying cause of hypernatremia
• Overestimating or underestimating total body water when calculating deficit

Despite a study suggesting that rapid correction may not increase mortality in critically ill patients 1, the consensus remains that gradual correction at rates not exceeding 0.5 mmol/L/hour is safest, especially for chronic hypernatremia 2, 3.